The present invention relates to compressors for compressing a working fluid, such as refrigerant, to a required pressure, and more particularly, to a compressor of which compression capacity changes with a direction of rotation.
The dual capacity compressor is a kind of reciprocating type compressor of which piston stroke as well as a compression capacity vary with an eccentric sleeve rotatably coupled to a crank pin of a crankshaft, a position of which with respect to the crank pin is dependent on a direction of rotation of the motor and the crankshaft. Since the dual capacity compressor has a compression capacity that can be varied with a required load, the dual compressor is used widely in apparatuses which require compression of working fluid, particularly in home appliances operative in a refrigeration cycle, such as a refrigerator, for enhancing an operation efficiency. A U.S. Pat. No. 4,236,874 discloses a general dual capacity compressor, referring to which a related art dual capacity compressor will be explained, briefly. FIG. 1 illustrates a section of a dual capacity compressor disclosed in U.S. Pat. No. 4,236,874, and FIG. 2 illustrates operation of the dual capacity compressor, schematically.
Referring to FIG. 1, the dual capacity compressor is provided with a piston 7 in a cylinder 8, a crankshaft 1, a crank pin 3 having a center 3a eccentric from a center of the crankshaft 1a, an eccentric ring 4 coupled on the crank pin 3, and a connecting rod 6 connected to the eccentric ring 4 and the piston 7, as key components. The eccentric ring and the connecting rod 6 are rotatable both with respect to the other, and the center 3a of the crank pin. There are release areas 9 in contact surfaces of the crank pin 3 and the eccentric ring 4, and a key 5 for coupling the crank pin 3 and the eccentric ring 4 together fitted in the release areas for coupling the crank pin 3 and the eccentric ring 4. The operation of the dual capacity compressor with respect to the compression capacity will be explained.
Referring to FIG. 2, in the dual capacity compressor, a stroke of the piston 7 is regulated by an eccentricity varied with a position of the eccentric ring 4, and, if a large capacity is required, the crank shaft 1 is rotated in a clockwise direction (regular direction) and, if a small capacity is required, the crank shaft 1 is rotated in a counter clockwise direction (reverse direction). In detail, FIG. 2A illustrates a moment the piston 7 is at a top dead center during a clockwise rotation, and FIG. 2B illustrates a moment the piston 7 is at a bottom dead center during a clockwise rotation, when the stroke Lmax is the greatest because the eccentricity is the greatest. And, FIG. 2C illustrates a moment the piston 7 is at a bottom dead center during a counter clockwise rotation, and FIG. 2D illustrates a moment the piston 7 is at a top dead center during a counter clockwise rotation, when the stroke Lmin is the smallest because the eccentricity is the smallest.
However, during the foregoing operation, the crank pin 3 and the eccentric ring 4 are involved in centrifugal forces, respectively caused by their rotation around the center 1a of the crank shaft, exerting on a point between the shaft center 1a and the pin center 3a, and a point on a line extended from the shaft center 1a to the a center of gravity of the ring 4a, respectively. Therefore, different from FIGS. 2A and 2B, as lines of actions are not one the same line, a local rotating moment is occurred at the eccentric ring 4 as a product of a vertical distance xe2x80x98dxe2x80x99 to the pin 3 and its own centrifugal force, acting in a direction the same with a direction (counter clockwise direction) of rotation of the crank shaft 1. Since the crank pin 3 and the eccentric ring 4 are members that can make relative movement to each other, the rotating moment causes a relative rotation of the eccentric ring 4 in a direction of rotation of the crank shaft 1, releasing the key 5 from the crank pin 3 and the eccentric ring 4, and leaving the eccentric ring 4 and the key 5 to move together as shown in FIG. 3.
Moreover, as shown in FIG. 3, during operation, for an example, in the clockwise direction, a pressure xe2x80x98Pxe2x80x99 (a pressure of re-expansion of the working fluid) in the cylinder after compression pushes the eccentric ring 4 to a direction of rotation of the crank shaft 1, to cause the eccentric ring 4 to make a relative rotation with respect to the crank pin 3 in a rotation direction of the crank shaft. At the end, such a relative rotation makes operation of the compressor unstable, and performance of the compressor poor.
In fact, the relative rotation is occurred because the key 5 can not fix the crank pin 3 and the eccentric ring, perfectly. The key 5 rolls within the release area whenever the direction of rotation of the crank shaft is changed, to cause serious wear at respective contact surfaces, that shortens a lifetime of the compressor.
In the meantime, other than the U.S. Pat. No. 4,236,874, there are many patent publications that disclose technologies of the dual capacity compressors, which will be explained, briefly.
Similarly, U.S. Pat. No. 4,479,419 discloses a dual capacity compressor provided with a crank pin, eccentric cam and a key. The key is fixed to the eccentric cam, and moves along a track in a crank pin when a direction of rotation of the compressor is changed. However, since the key can not fix the crank pin and the eccentric cam perfectly, the U.S. Pat. No. 4,479,419 also has unstable operation caused by the relative rotation.
U.S. Pat. No. 5,951,261 discloses a compressor having an eccentric part with a bore of a fixed inside diameter formed across the eccentric part, and an eccentric cam with another bore with a diameter the same with the eccentric part formed at one side thereof. A pin is provided to the bore in the eccentric part, and a compression spring is provided to the bore in the eccentric sleeve. Accordingly, when the bores are aligned during rotation, the pin moves to the bore in the cam by a centrifugal force, that couples the eccentric part and the eccentric cam, together. However, since the U.S. Pat. No. 5,951,261 is provided with only one bore in the eccentric cam, the U.S. Pat. No. 5,951,261 can couple the eccentric part and the eccentric cam together only when the compressor rotates in a particular direction. Moreover, an operation reliability can not be secured, since an exact movement of the pin from the eccentric part to the cam through respective bores is difficult.
Accordingly, the present invention is directed to a dual capacity compressor that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a dual capacity compressor which can maintain a fixed eccentricity and make a stable operation even if the compressor is rotated in any directions that have different compression capacity.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
As explained, the inventor understands that the unstable operation of the dual capacity compressor is caused by a local centrifugal force of the eccentric sleeve, and an external load through the connecting rod and etc., during operation. Though such causes are not avoidable as far as an eccentric mechanism is used, the inventor understand that, if the crank pin and the eccentric sleeve can be fixed positively during operation, such a problem can be solve. Taking an idea of a key member that has such a fixing structure, the key member and members related thereto are modified as follows so that the relative motion between the crank pin and the eccentric sleeve can be prevented.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the dual capacity compressor includes a power generating part including a reversible motor and a crank shaft inserted in the motor, a compression part including a cylinder, a piston in the cylinder, and a connecting rod connected to the piston, a crank pin in an upper part of the crank shaft eccentric to a center of the crank shaft, an eccentric sleeve having an inner circumferential surface rotatably coupled on an outer circumferential surface of the crank pin, and an outer circumferential surface for rotatable coupling of an end of the connecting rod, and a key member for making the eccentric sleeve to be caught at the crank pin completely in both clockwise and counter clockwise direction rotation of the motor.
Preferably, the key member is in contact with the eccentric sleeve at a plurality of points, and more preferably, at two points set up with reference to a center line in any direction during operation.
Preferably, the key member includes a first projection for projection for a length from the crank pin even when the compressor is not in operation, and a second projection for projection for a length from the crank pin when the compressor is in operation, and for doing this, it is more preferable that a distance between ends of the first and second projections has a length greater than an outer diameter of the crank pin.
The crank pin includes one pair of key member fitting parts formed opposite to each other oriented on a sloped extension line with reference to a horizontal plane.
The key member fitting part may be a pass through hole formed in a wall of the crank pin or at least one slot extended from a position of the wall of the crank pin to a top thereof. It is preferable that the crank pin is extended higher than the eccentric sleeve.
The eccentric sleeve includes a track part formed along a circumference thereof for facilitating rotation of the eccentric sleeve itself relative to the projection of the key member, and a limiting part formed relative to the track part for limiting rotation of the projection of the key member.
The track part of the eccentric sleeve may be a pass through hole extended for a length along a circumferential direction at a depth from a top thereof, or a cut away part extended along a circumferential direction at a depth from the top.
It is preferable that the steps formed between the track part and the limiting part are parallel to an extension line connecting a center of rotation of the crank shaft and a center of the crank pin, and, more preferably, spaced as much as a half of a thickness of the key member. The steps may be sloped at an angle with respect to an extension line connecting the rotation center of the crank shaft and the center of the crank pin. The eccentric sleeve may further include oil supply holes formed opposite to each other at a height.
The key member includes a first projection projected for a length from the crank pin and engaged with one step on the eccentric member, a stopper for limiting a length of projection of the first projection, and a second projection projected opposite to the first projection during rotation and engaged with the other step of the eccentric sleeve.
Preferably, the first and second projections of the key member have the same thickness, and have sections of circular, rectangular, or hexagonal. Preferably, the first projection has a length of projection from an outer circumference of the crank pin greater than a half of a width of the step, and the second projection has such a length that an end thereof is not projected from the outer circumference of the crank pin when the compressor is not in operation.
The first stopper may have a crank pin contact surface in conformity with an inner circumferential surface of the crank pin, or be of a separable type.
The separable type first stopper may be inserted in a circumferential groove in the key member and fixed by a fixing member.
The key member may further include an elastic member for supporting the key member such that a part of the key member is kept projected out of the crank pin regardless of operation of the compressor, and for doing this, the stopper further includes a receiver for the elastic member.
It is preferable that the key member may further include a second stopper for limiting a length of projection of the second projection out of the crank pin according to a direction of action of the centrifugal force. The second stopper may be a hollow tube member movably fitted in a longitudinal direction of the second projection, a longitudinal extension of the first stopper having a diameter greater than a diameter of the second projection, or a radial direction extension of the second projection having a thickness.
Thus, the present invention can prevent a relative rotation between the crank pin and the eccentric sleeve, thereby enhancing a stable operation and efficiency of the compressor.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.